Small Molecule Donor/Polymer Acceptor Organic Solar Cells with Efficiency of 13.65% Enabled by Film Formation Kinetics and Phase Separation Control.

Organic solar cells (OSCs) based on small molecular donor and polymer acceptor (S/P-type) show low photovoltaic performance due to the unideal morphology. However, previous work mainly focused on the aspects of donors, but how the polymer acceptor influences its morphology and device performances is lacking in study. In this work, we apply three polymerized nonfullerene small molecules as acceptors, combining film-forming kinetics and microstructure characterization to investigate the efficient S/P-type OSCs requirements on polymers. We found the following two results: Strong miscibility between donor and acceptor would facilitate the acceptor inducing the donor to adopt a face-on packing; under similar miscibility, the inferior crystallinity of the acceptor facilitates a more proper phase separation. Hence, the DTBDT-C3-D6:PY2S-F-based S/P-type OSCs with the best miscibility achieve an impressive PCE of 13.65% with both high short-circuit current density (Jsc) of 20.73 mA cm and fill factor (FF) of 72.93%, which are among the highest values in the reported binary S/P-type OSCs so far. Our work provides a new perspective for the development of highly efficient S/P-type OSCs with polymer acceptor matched to small molecule donor.